Heretofore, corner pieces for use in building construction, or for the assembly of partitions or the like, were either fabricated at the erection site from available materials or comprised prefabricated members which were manually held in place while being assembled with the structure and secured in fixed relation to the building structure. Corner pieces of sheet metal have been utilized to provide a closure at such positions and metal angle sections, or other formations, have been used to frame a corner, but with these prior arrangements it has been necessary physically to maintain such members in proper relation to the supporting structure while the member was being secured. Such practices were time consuming and frequently difficult and consequently expensive from the standpoint of labor and the man hours involved in completing structures of this type.